(USA TODAY) -- A family of "nightmare" superbugs - untreatable and often deadly - is spreading through hospitals across the USA, and doctors fear that it may soon be too late to stop them, senior health officials said Tuesday.

"These are nightmare bacteria that present a triple threat," said Thomas Frieden, director of the Centers for Disease Control and Prevention. "They're resistant to nearly all antibiotics. They have high mortality rates, killing half of people with serious infections. And they can spread their resistance to other bacteria."

So far, this particular class of superbug, called carbapenem-resistant Enterobacteriaceae, or CRE, has been found only in hospitals or nursing homes, rather than in the community, Frieden said. But officials sounded the alarm partly because, if the bacteria's spread isn't contained soon, even common infections could become untreatable.

The superbug tends to strike immune-compromised people who are hospitalized for a long time or living in a nursing home, Frieden said. And CRE doesn't spread easily from person to person, like the bacteria causing pink eye or strep throat.

These superbugs are "the biggest threat to patient safety in the hospital that we have," said Costi Sifri, an infectious disease physician and hospital epidemiologist at the University of Virginia Health System. "Unfortunately, it doesn't seem like anything is slowing their spread."

In 2001, only 1.2% of the common family of bacteria, Enterobacteriaceae, were resistant to carbapenem antibiotics - the strongest class available. By 2011, that figure had jumped to 4.2%.

In the first half of 2012, nearly 200 hospitals treated at least one of these infections, Frieden said. About 4% of hospitals have had at least one patient with CRE, along with 18% of long-term, acute-care hospitals, the CDC said.

Those numbers could underestimate the scope of the problem, however. There are no reliable national data on CRE infections. There is no national requirement that hospitals and other health care facilities report CRE cases. CDC officials noted Tuesday that only six states require hospitals and other health care facilities to report CRE infections.

In November, USA TODAY reported that CRE infections already are endemic in several U.S. population centers, including New York, Los Angeles and Chicago, which account for hundreds of confirmed cases. Smaller pockets of cases have been reported across much of the country, including Oregon, Wisconsin, Minnesota, Pennsylvania, Maryland, Virginia and South Carolina.

Hospitals have fought these infections for years.

An outbreak of the bacteria Klebsiella pneumoniae killed seven patients between 2011 and 2012 at the National Institutes of Health.

Now, with the superbugs found in 42 states, Frieden said he felt it was time to warn the public.

The country has only a narrow "window of opportunity" to act before it's too late to halt the superbugs' spread, Frieden said.

When antibiotics no longer help a patient, doctors are resorting to alternatives, such as surgery to cut out infected tissue, said Sifri, who added that the country could be entering the beginning of the "post-antibiotic era."

Neil Fishman, associate chief medical officer at the University of Pennsylvania Health System, said doctors are now considering using old, outdated antibiotics that can damage the kidneys, because safer ones no longer work.

"I've had to ask patients, 'Do you want a toxic antibiotic and end up on dialysis, or would you prefer to have a limb amputated?' " Fishman said.

Perhaps the greatest threat from CRE is its ability to share its resistance genes with other bacteria. So although CRE's spread is somewhat limited today, it could potentially share its resistance with far more common bacteria, such as E. coli, Frieden said.

If that happened, common conditions affecting millions of Americans, which are now treated with antibiotics - such as diarrhea, urinary tract infections, respiratory conditions and pneumonia - could become untreatable.

"It's not very often that our scientists come to me and say, 'We have a very serious problem and we need to say something to save lives,' but that is what is happening," said Frieden, who outlined a six-step plan for hospitals, called "Detect and protect."

First, hospitals need to find out which, if any, of their patients have CRE, including patients transferred from other facilities. They should take precautions, such as wearing gloves and gowns, to prevent spreading the superbug, even dedicating separate rooms, machines and staff for those infected, Frieden said.

Hospital staff should remove invasive devices, such as catheters, as soon as possible. These devices can spread the superbug deep into the body, Frieden said. Lastly, doctors need to prescribe antibiotics more judiciously. About half of antibiotic prescriptions are either unnecessary or inappropriate, he said. Patients also should avoid asking for antibiotics, because many common illnesses, such as ear infections and sinus infections, usually go away without them.

"We can't afford to wait until a large-scale outbreak occurs to fight these dangerous bacteria," said Sara Cosgrove, who serves on the board of Society for Healthcare Epidemiology of America. "Excessive antibiotic use combined with failure of health care workers to wash hands before and after caring for patients allows these bugs to develop and spread."

Patients and their families can help, too, by reminding everyone who enters the hospital room to wash their hands, Frieden said. Patients also should speak up if they have recently been in another hospital or foreign country, said Helen Boucher, a board member of the Infectious Diseases Society of America.

There is little chance that an effective drug to kill CRE bacteria will be produced in the coming years. Manufacturers have no new antibiotics in development that show promise, according to federal officials and industry experts, and there's little financial incentive because the bacteria adapt quickly to resist new drugs.

Boucher praised Frieden for educating the public.

"It's an issue of public health," Boucher said. "We all have to be part of the solution."